1. Field of the Invention
The present invention generally relates to force generating apparatus and, more particularly, is directed to a force generating apparatus such as a torquer or the like which is for use with a gyro apparatus such as a gyro compass and so on.
2. Description of the Prior Art
A conventional force generating apparatus of the above-mentioned kind will be described with reference to FIGS. 1A through 1D. FIG. 1A shows a plan view of the above-mentioned force generating apparatus according to the prior art, FIG. 1B shows a side view thereof, FIG. 1C shows a front view of a movable member used in this force generating apparatus, and FIG. 1D shows a structure of a magnet assembly member also used in this force generating apparatus.
Referring to FIG. 1A, a stator 500 will be described initially. As illustrated, an iron core 501-2 of U-letter configuration is formed by laminating plate-shaped magnetic materials, and permanent magnets 501-3a, 501-3b are attached to the iron core 501-2 in the polarity such that magnetic fluxes produced by these permanent magnets 501-3a, 501-3b are communicated therethrough to form a permanent magnet assembly member 501-1. An excitation unit assembly component 501 is formed by winding excitation coils 501-4a, 501-4b around the above permanent magnet assembly member 501-1. The stator 500 is formed by fastening the excitation unit assembly component 501 and an iron core 502 of U-letter configuration made of the same material and size of those of the iron core 501-2 on a supporting member 520 by screws (not shown) such that the iron core 501-2 of U-letter configuration and the iron core 502 are opposed at their protruded portion end faces to each other with constant spacings 540-1, 540-2. Further, a mount 530 is attached to the supporting member 520. A movable member 510 is composed of a conductor 510-1 of an open square configuration (hereinafter referred to as a force coil) and a bracket 510-2 which supports the force coil 510-1.
When this force generating apparatus is applied, for example, to the gyro compass in actual practice, the stator 500 is attached to a first member (e.g., gyro case or the like) to which the force of the force generating apparatus is applied, and the movable member 510 is attached to a second member which is a supporting device for supporting the first member such that the first member becomes rotatable in a certain range. At that time, portions 510-1a, 510-1b (see FIG. 1C) forming one part of the force coil 510-1 are respectively located substantially at the center of the spacings 540-1, 540-2 formed in the stator 500, whereby the stator 500 and the movable member 510 can be constantly kept in the non-contact state against a necessary relative displacement.
Magnetic fluxes .phi..sub.1, .phi..sub.2 (.phi..sub.1 =.phi..sub.2) are respectively produced in the spacings 540-1 and 540-2 by the permanent magnets 501-3a, 501-3b (see FIG. 1D). If now a current i is flowed to the force coil 510-1, then a force is produced between the movable member 510 and the stator 500 due to Fleming's left-hand rule.
As shown in FIG. 1, the excitation coils 501-4a, 501-4b are adapted to superimpose AC magnetic fluxes to those generated by the permanent magnets 501-3a, 501-3b in the spacings 540-1, 540-2 so that the force generating apparatus is rendered a pickup function. This pickup function of the force generating apparatus is not directly related to the present invention and therefore need not be described. At that time, the conductor 510-1 serves also as a pickup coil in addition to the force coil.
However, according to the above-mentioned conventional force generating apparatus, a total sum of magnetic moments caused by the permanent magnets is not cancelled out as zero so that, when an external magnetic field is applied to this force generating apparatus, then the force generating apparatus generates a torque equal to geometric product of the whole magnetic moments of the magnet assembly member, intensity of external magnetic field and cosine of an angle formed by magnetic axes of the respective permanent magnets and the external magnetic field. This torque is a harmful torque which is irrelevant to the torque generated by the current flowed to the force coil.
As, for example, shown in FIG. 1D, the magnet assembly member 501-1 forms a magnet of a horseshoe configuration on the whole. As a result, the magnet assembly member 501-1 has a magnetic moment whose magnetic axis is extended in the direction shown by an arrow M in FIG. 1D on the whole. Further, as the whole of the stator 500, the magnetic moment is slightly reduced due to the existence of the U-letter shaped iron core 502 as compared with the case such that the U-letter shaped iron core 502 is not provided. However, due to the existence of the spacings 540-1, 540-2, the above magnetic moment cannot be cancelled out as zero. There is then the disadvantage that the conventional force generating apparatus is caused to generate the above harmful torque by the external magnetic field applied thereto.